Fas and caspase-8 are not involved in p21-IRS–induced apoptosis. (A) U937 cells were incubated with SM1/23, a mAb that disrupts Fas-mediated apoptosis, prior to the addition of p21-IRS or CH-11. (B) Jurkat cells overexpressing CrmA or transfected with the expression vector were treated with p21-IRS, staurosporine, or CH-11 for 3 hours, 4 hours, or overnight, respectively, and apoptosis determined.